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Dr. Hamman
Dr. Hamman, Technician
Category: Classic Car
Satisfied Customers: 6286
Experience:  I have 30 years experience repairing, restoring, and customizing cars, and pickup trucks.
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I have a 71 Cougar with a 351 cleveland 2v. It starts up

Customer Question

I have a 71 Cougar with a 351 cleveland 2v. It starts up fine when cold but when it's hot it runs rough and when I turn it off it won't start again. I've changed the Starter, coil, wires, plugs, rotor, distribur... And it's still won't start when hot. I had the car Rebuit as well and nothing has Changed...
Submitted: 2 years ago.
Category: Classic Car
Customer: replied 2 years ago.
carb is Rebuilt. And the problem is still the same. Starts fine when cold. Runs rough when hot then will not start when hot. It will Crank over and over, And seem to almost get started but will not. Could it be vapor lock? If so how do I fix that?
Expert:  Dr. Hamman replied 2 years ago.

Hi, I am a professional certified mechanic, with an engineering background,and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.

Vapor lock should happen when it is driving, and hot if it is the problem.I would check the fuel pressure and spark when it wont start. If it is vapor locked and you prime the carb with about a shot glass (1 oz) of gas, it should fire up and run just a few seconds with the pedal floored. If you are loosing spark the coil and condenser are suspect.If the problem is fuel the pressure test and taking a spark plug reading should tell you a lot. Go over all of this and if you have any more questions at all, I am hereto help. Good luck with it, have a great day, and Thanks for using Just Answer.

I do not get paid for my work unless you rate at 3 to 5 Stars, a bonusis always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further. My goal is to provide 5 star service, Thanks.

Expert:  Dr. Hamman replied 2 years ago.

If vapor lock is the problem fuel boils in the suction fuel line between the gas tank and the fuel pump. The best fix for vapor lock is to install an electric fuel pump in the rear near the tank. An electric pump will completely eliminate vapor lock.

Customer: replied 2 years ago.
If it's not vapor lock what do you suggest it could be? After I drive it for 20 minutes it starts to hesitate and when I put my foot on the gas and hesitates and it has a pop sound it hesitates and has a pop sound and so I park it and turn it off. After waiting about 10 15 minutes I'll get back in the car and try to start it and it'll crank, but it just won't start
Customer: replied 2 years ago.
what would you suggest the problem would be if it is not vapor lock... Favorite lock is just a suggestion that a parking lot mechanic told me. In your opinion what do you think it sounds like it is?
Expert:  Dr. Hamman replied 2 years ago.

It could be spark or fuel causing the problem. I would absolutely 100% want to check the spark and fuel pressure when it wont start. That will point you in the right direction. It could be a coil failing, or fuel problems. If you like we can talk on the phone, I am available tonight.

Customer: replied 2 years ago.
It doesn't seem to be a fuel or spark issue....
Customer: replied 2 years ago.
It's not the gas or the spark, and has plenty of spark and it has plenty of gas getting to the carburetor. I can tell you this, it seems to have a miss when it's idling. But it definitely has gas and it definitely has spark
Expert:  Dr. Hamman replied 2 years ago.

Just be sure about the fuel and spark, assuming anything can lead you away from the problem. It is possible that it is flooding after hot shutdown. Pulling a spark plug to see if it is wet with fuel when it wont start can tell you if it is flooding after shutdown. Beyond fuel and spark you might want to perform a compression test. I have seen engines with low compression that had trouble starting hot. If this is the case starting fluid should allow it to start when hot. Compression, or leak down tests will spot this problem. If you have any more questions at all, I am hereto help. Good luck with it, have a great day, and Thanks for using Just Answer.


Customer: replied 2 years ago.
It's not the fuel. It's not the spark. Plugs are dry when it's hot. "Ouch". By the way. Still have no clue what it is...
Expert:  Dr. Hamman replied 2 years ago.

If the fuel and spark are not at fault which would be unusual, then odds are the engine has an internal problem. I would preform a leak down test on it and see if there is excessive leakage. Some engines with this type of problem cant build enough compression when hot to restart. You would be looking for tight valves, or piston rings that allow too much pressure to get around them. An engine doing this can seem to run good, but just be a pain to fire up hot. Perform the leak down test see what it says. Look at the strength and color of the spark when it is cold, and when it is hot. If the plugs are dry, try priming it with about a shot glass of gas and hold the pedal on the floor to see if it will start. If you have any more questions at all, I am hereto help. Good luck with it, have a great day, and Thanks for using Just Answer.